In recent publications the principal investigator has described the preparation of novel organolithium and organomagnesium reagents, which are capable of introducing into molecules functinal groups that can serve as alkylating agents. The plan of research is to employ such organometallics to affix potential antitumor alkylating agents, such as epoxide, aziridine, vinylsulfonyl, acetylenylsulfonyl, cyclopropylsulfonyl and lactone functions, to nitrogen heterocycles of recognized biological importance. The acidic (indoloid) or basic (pyridinoid) nature of the parent heterocyclic nucleus should permit the bioactivation of the appended alkylating unit by protonation, quaternization or deprotonation at the heterocyclic nitrogenm. Furthermore, many of the appended groups, such as vinylsulfonyl or epoxide units, should be capable of forming adducts in vitro with mercaptans and amines. Such adducts may then be compatible forms for administering such antitumor drugs, which would then undergo unmasking in vivo by eliminating r2NH or RSH and thereby regenerating the potent antitumor alkyhlating agent. This use of masked alkylating agents would represent another form of bioactivation.